It was specifically because of being an old member that Burgess was given command of first ship.
"One of the very first to join the crew."
And... that ISN'T important?!?!
Who was the first guy to join Roger's crew?
Who was the first guy to join Luffy's crew?
Burgess could be #3, but the idea that he's actually beneath Shiryu is ridiculous.
The fact that he's been working with Blackbeard for so long, while having control of the 1st Ship, PROVES HIS IMPORTANCE.
Most great pirates meet their right hand men early, not halfway through forming their crew.